1. Field of the Invention
This invention is in the field of powder metallurgy and forging and involves the manufacture of alloy steel annular bearing elements from cold (room temperature) forged sintered powder metal preforms, using a homogeneous mix of ferro-alloy and iron powders.
2. Description of the Prior Art
At the present time, most ball, roller and needle bearing rings are made from wrought alloy steel tubing, bar stock or plate. Generally, the steel compositions are manufactured in electric furnaces with air melting. For increased bearing life, more highly refined steels or increased alloy content are being used. There are further means provided to enhance bearing life such as by forging ring blanks, special heat treatments, and various mechanical cold working processes.
In recent times, patents have been granted for the manufacture of sintered powder metal annular bearing rings. Some of these are directed to powder metal bearing rings which achieve increased bearing life from local densification, particularly in the region of the raceway. Other patents teach hot forging the ring blank to increase the bearing life. All of the powder metal rings described in this prior art use or prefer to use pre-alloyed metal powders which require comparatively high compacting pressures and increased material cost.
U.S. Pat. No. 3,626,564 to Daniel describes the manufacture of ball bearing races by rolling an annular body within a sizing ring which is initially undersized. The annular body is rolled within a sizing ring by a small internal roll having an external rib shape to produce the channel at the inner surface of the bearing race. As the rolling continues, the radial dimension of the bearing race decreases with a corresponding increase in its diameter until it completely fills the sizing ring. Then the excess stock is extruded axially at one side only of the race, with the opposite side being restrained by a flange on the sizing ring.
Chmura et al U.S. Pat. No. 3,782,794 is one of the patents dealing with antifriction bearing rings produced from powder metal. In the method there described, a sintered, porous powder metal annular blank is formed with a bearing raceway on a circumferential face by mechanically working a selected area of the face to a suitable depth, thereby producing a dense zone adjacent to the bottom of the raceway, while retaining the remaining portion of the sintered metal as a substantially porous structure having a relatively low density.
In U.S. Pat. No. 3,867,751 Connell et al describe the formation of inner and outer bearing rings by roll forming of a sintered metal blank which densifies the ring in the bearing areas.
U.S. Pat. No. 3,874,049 to Ferguson describes a method of forming powder metal parts into bearings in which a sintered preform is cold formed and during such forming shear forces are applied to the surface of the preform in the area of the bearing surface by means of a movable die which penetrates and wipes along the bearing surface area of the preform.
U.S. Pat. No. 3,992,763 to Haynie et al describes a method of making powder metal bearings in which a briquetted powder metal preform is carburized prior to hot forging to substantially increase the initial carbon content and the forged part is cooled by quenching to obtain a predetermined case depth.
Another method of making a forged powder iron article is described in Sarnes et al U.S. Pat. No. 4,002,471. In this disclosure, a pre-alloyed metal powder is compressed into a preform which is sintered and then heated to a temperature above its austenizing temperature. While the preform is at this temperature, it is hot forged and then cooled to its austenizing temperature whereupon it is quenched to produce the finished article.
Zambrow et al U.S. Pat. No. 4,006,016 describes a method of forming powder metal into structural parts wherein pre-alloyed steel powder is pressed into a preform, compacted, and then heat treated. The preform is at a temperature of 2100.degree. F. when it is hot forged in a preheated forming die to produce a metal part having a density in excess of 99% of theoretical density.
U.S. Pat. No. 4,051,590 to Halter et al deals with an automated method of hot forging articles from powder metal preforms in which the preforms are automatically passed through an induction heating device, and then to a pair of dies where they are forged into finished articles. This disclosure is directed essentially to the method of automating the hot forging operation.
Finally, Chmura et al U.S. Pat. No. 4,059,879 describes a method said to be suitable for the production of annular bearing rings in which a sintered porous powder metal compact is partially densified while other portions of the powder metal body are confined so as to inhibit growth of the powder metal body during working and inhibiting cracking.